Compatible AM quadrature stereo systems in which the distortion caused by quadrature sidebands in a mono envelope detector is cancelled by predistortion of the signal sum by negative feedback at the transmitter.
In the prior art modified quadrature systems reduce the signal-difference amplitude by more than 11 dB, to secure reasonable freedom from harmonic distortion in a mono receiver with an envelope detector, and use synchronous sampling at the receivers. Other prior art stereo systems reduce the distortion by a material increase in complexity of the transmitting and receiving apparatus.
This invention discloses quadrature stereo systems which transmit a quadrature stereo wave, altered by negative feedback so that distortion in a mono receiver with an envelope detector, due to the quadrature sidebands, is significantly reduced. The stereo receivers use envelope and angle modulation detectors for separation of the signals, and sampling and reconstruction means for reduction of the noise.